Wed·Mar 31, 2021Wednesday·March 31, 2021

1. 01*

   New Experimentally Observable Gamma-ray Emissions from 241Am Nuclear Decay

   Katrina E. Koehler · Michael D. Yoho · Matthew H. Carpenter · Mark P. Croce · David J. Mercer · Chandler M. Smith · Aidan D. Tollefson · Duc T. Vo · Michael A. Famiano · Caroline D. Nesaraja · Daniel T. Becker · Johnathon D. Gard and 7 other authors

   With the high resolution of microcalorimeter detectors, previously unresolvable gamma-ray lines are now clearly resolvable. A careful measurement of Am-241 decay with a large array of gamma-ray microcalorimeters has revealed never before seen or predicted gamma lines at 207.72 +/- 0.02 keV and 208.21 +/- 0.01 keV. These results were made possible by new microwave-multiplexing readout to increase the array size and improved analysis algorithms to eliminate spectral artifacts. We suggest nuclear levels from which these gamma-rays might originate and calculate branching ratios for these transitions from measurements of both mixed Pu-Am standards and a pure Am-241 source. These results have implications for nuclear material safeguards and accounting, particularly for microcalorimeter gamma spectrometers, which are now being adopted in nuclear safeguards analytical laboratories.

   nucl-ex1 citation
2. 02*

   Causality violations in realistic simulations of heavy-ion collisions

   Christopher Plumberg🇺🇸 · Dekrayat Almaalol🇺🇸 · Travis Dore🇺🇸 · Jorge Noronha🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸

   Causality is violated in the early stages of state-of-the-art heavy-ion hydrodynamic simulations. Such violations are present in up to 75% of the fluid cells in the initial time and only after 2-3 fm/$c$ of evolution do we find that 50% of the fluid cells are definitely causal. Superluminal propagation reaches up to 15% the speed of light in some of the fluid cells. The inclusion of pre-equilibrium evolution significantly reduces the number of acausal cells. Our findings suggests that relativistic causality may place constraints on the available parameter space of heavy-ion collision simulations when factored into more thorough statistical analyses.

   ↳ nucl-thhep-phnucl-exPRC(2022)·76 citations
3. 03*

   Heavy+light pseudoscalar meson semileptonic transitions

   Zhen-Ni Xu🇨🇳 · Zhu-Fang Cui🇨🇳 · Craig D. Roberts🇨🇳 · Chang Xu🇨🇳

   A symmetry-preserving regularisation of a vector$\times$vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving $\pi$, $K$, $D_{(s)}$, $B_{(s,c)}$ initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu-Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured $B_{s,c}$ branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on $B_{(s)}\to D_{(s)}$ transitions yield a prediction for the Isgur-Wise function in fair agreement with contemporary data.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJC(2021)·17 citations
4. 04*

   Leading jets and energy loss

   Duff Neill🇺🇸 · Felix Ringer🇺🇸 · Nobuo Sato🇺🇸

   The formation and evolution of leading jets can be described by jet functions which satisfy non-linear DGLAP-type evolution equations. Different than for inclusive jets, the leading jet functions constitute normalized probability densities for the leading jet to carry a longitudinal momentum fraction relative to the initial fragmenting parton. We present a parton shower algorithm which allows for the calculation of leading-jet cross sections where logarithms of the jet radius and threshold logarithms are resummed to next-to-leading logarithmic (NLL${}^{\prime }$) accuracy. By calculating the mean of the leading jet distribution, we are able to quantify the average out-of-jet radiation, the so-called jet energy loss. When an additional reference scale is measured, we are able to determine the energy loss of leading jets at the cross section level which is identical to parton energy loss at leading-logarithmic accuracy. We identify several suitable cross sections for an extraction of the jet energy loss and we present numerical results for leading subjets at the LHC. In addition, we consider hemisphere and event-wide leading jets in electron-positron annihilation similar to measurements performed at LEP. Besides the average energy loss, we also consider its variance and other statistical quantities such as the KL divergence which quantifies the difference between quark and gluon jet energy loss. We expect that our results will be particularly relevant for quantifying the energy loss of quark and gluon jets that propagate through hot or cold nuclear matter.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·32 citations
5. 05*

   The quest for the proton charge radius

   Istvan Angeli🇭🇺

   A slight anomaly in optical spectra of the hydrogen atom led Willis E. Lamb to the search for the proton size. As a result, he found the shift of the 2S1/2 level, the first experimental demonstration of quantum electrodynamics. In return, a modern test of QED yielded a new value of the charge radius of the proton. This sounds like Baron Muenchausens tale: to pull oneself out from the marsh by seizing his own hair. An independent method was necessary. Muonic hydrogen spectroscopy came to the aid. However, the high-precision result significantly differed from the previous, electronic, values: this is the proton radius puzzle. This puzzle produced a decade-long activity both in experimental work and in theory. Even if the puzzle seems to be solved, the precise determination of the proton charge radius requires further efforts in the future.

   ↳ physics.hist-phhep-phnucl-exquant-ph1 citation

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.